I'm getting ready to put together my first NFT system. I have a question about lighting though. I have two T-8 4' dual bulb fixtures. I also have four natural light tubes to match. They're 34 watt fixtures. I plan to use these lights on seedlings in rockwool shortly. The system I'm planning is either one or two 8' sections of 4" pvc with 3" holes on top every 12" or 18". I'm thinking tomatoes and something else that matches high nutrient levels, maybe peppers.

So my question is, when will I hit the wall with light? I suspect that these fixtures will work just fine on the seedlings, but will not be enough later. I'm not sure what the spread is for these. I could run 1 8' section of pvc and put the lights over that. Or I could put a second pipe and have the water do a u-turn to come back to the bucket and position the lights in between the two pipes. Can someone give me a feel for how much light I will need for a given number of plants, etc.?

It will be in the basement, so assume no ambient light. thanks

brian